Investment material



Patent Dec. 4, E23.

TUE MARSHALL TECINTOSH, 0F SYDNEY, AUSTRALIA.

DIVESTEEENT TERIAL.

no Drawing.

To aZZ whom it may concem! c it known that I, ARTHUR MARSHALL MoINTosH, a citizen of the Commonwealth of Australia, and a resident of Sydney, Australia, have invented a certain new and useful Investment Material, of which the following is a specification.

y invention consists in an investment material to be used for making moulds in all cases where the article to be produced must be subject to intense heat for the purposes of fusing, and accurac of shape and fit is essential, and particu arly, where it is required that a separate and distinct mould be employed in each individual case. The investment material is of particular value in the moulding of porcelain and other ceramic ware for dental and other purposes. It may also be used in the moulding of glass and other materials which may be shaped in a fused condition.

1V y investment material which is to be own as pyroplastic consists of a mixture of silica, and a bonding material such as alumina or alumina bearing clay. Both ingredients are mingled in a pulverized condition. The silica particles may be of such size as would permit of their passing through a sixty mesh sieve or screen, and the alumina particles should be ground as finely as possible. It is not intended, how ever that the particles of the ingredients she always be of the exact dimensions ,suggested, as an size is permissibib from the value and ment material. The gredient must be suc is subjected to heat the contraction of the alumina or alumina bearing material is compeilisated by the expansion of the silica partic e.

The entire mass, when subjected to intense heat, experiences no appreciable change in its size. In other words, my investment material will not contract or expand and thus alter the size of the mould and impair the accuracy of the article being formed to any appreciable degree.-

he proportions of the ingredients are reasonable variation in and would not detract efficiency of the investroportions of each in- Applieation filed July 15,;

that when the mass" 1922. Serial No. 575,386.

not susceptible of precise definition, since all clays have an alumina content in var ing degree and differ from one another 111 their chemical and physical properties. The proportions are ascertained, and can be ascertained by any one skilled in the art, by simple experiments upon the respective ingredients employed.

In my investment material, the clay or alumina bearing ingredient is mixed with the silica only in such proportions as are necessary to give cohesion to the mass. In other words, an alumina content effective as a bonding material is suflicient to compensate the expansion of the silica particles durin the application of'intense heat.

nvestment materials heretofore employed for the purposes of dentistry have usually been composed of silica and plaster of Paris.

This composition is deficient in porosity, and does not readily absorb water. If it isattempted to d the water out rapidly the material is liab e to explode. The thermal resistance is low, and when subjected to relatively moderate heat it becomes extremely fragile, and there is always a tendency to lose its original form. Such investment materials are therefore poorly adapted to dental and other purposes where precision and accuracy are imperative.

My investment material has considerable porosity; its thermalresistance is high, and it will not alter its size or shape by traction or expansion under heat. v

The advantages resulting from these physical properties are that it will readily absorb water, and may be rapidly dried without danger of explosion. Its high thermal resistance enables it to gain strength, and endure greater pressure when subjected to intense heat, as is necessary when articles are being fused in moulds in which it is employed. The fact that it will not change its shape or size under the application of intense heat insures accuracy of fit in the article being moulded and fused.

A further use to which my investment material may be put and purpose for which it is intended is to hold pieces of metalduring the proces of soldering as is now yv means of cuttle-fish in the jewelry manufacturing indust and other arts. y investment material as advantages over cuttle-fish in that itsoriginal cost is less,

of the fact that it is more easily shaped to the form of mould, and it can be repeatedly used.

For example, my investment material may be mixed with water and formed into die members between which porcelain or other ceramic substances maybe shaped either at the fusing point or at such other temperatures as will induce pliability or plasticity in the substance. During this forming or shaping process, and when subject to considerable pressure at the temperatures indicated, the pyroplastic mould will retain. its size and shape, and maintain its mechanical strength and cohesive properties. The particles of the investment material will not fuse. together or to the porcelain ware during this. process, and after being cooled the investment material may be readily broken away without injury to the ware.

The physical properties of my investment vmaterial consist in a high thermal resistance enabling it to withstand fusion at a temperature at which porcelain or ordinary ceramic ware will fuse and to retain its mechanical strength and cohesive properties, by reason the contraction of the particles composing the bonding material is offset by the expansion of those of the silica. It is readily moulded when water is admixed, and the moisture may be rapidly removed without danger of explosion. upon completion of the moulded article the investment material may be easily broken away without injury to the finished product, all of which assure a racy. in -the manufactured product and diminish the danger of injury to delicate or fragile ware.

The properties and value of my investment material may be explained and illustrated by describing one or two of the many processes in which it may be employed to effect important commercial results with a material saving of time and expense, and an increased accuracy in the finished product. It is of especial value in making porcelain inlays in the practice of dentistry.

For the making of such inlays, a wax model is prepared and embedded in my investment material. The-wax is then burned out, whereupon a mold of the exact size of the wax model will be left. A thin layer of porcelain mixed with water is then painted over the interior and edges of the mold. The investment material mold with the porcelain therein is placed in a furnace and the porcelain is fused. The mold and porcelain are then slowly cooled, and the ceramic subtance again applied so that the material is made to stand above the mould except at the edges, toallow for shrinkage. The porced members spaced apart slightly high degree of accu-.

lain is again fused and the process may be again repeated until the inlay is of the required size and shape.

In making dentures and more elaborate restorations I am likewise able to efiect similar economies by the employment of my investmentmaterial.

I The most enerallyapproved andaccepted practice the teeth-on a platinumplate by means 0 platinum pins. This is expensive, requires a high degree of skill and the results are uncertain.

Where my investment material is employed a model of the denture is made in the wax, and prepared porcelain teeth mounted on the wax model. he wax model with the teeth attached is then embedded in a-body of my investment material, leavingone surface of the ware exposed. The investment material is painted with a parting material for as required the mounting of which purpose my pyroplastic investment material may 'also be employed, and an upper mold or die member is made of themvestment material to fit the exposed surface of the model. The two die members made of the investment material are placed together and dried and then heated until out. Two die members are thus made formin%a perfect model.

orcelain mixed with water is placed in the mold members and is made to stand out beyond the deeper mold member. The mold by reason of the projecting or built up portion of the porcelain are then placed in the furnace. The mold member, which holds the teeth that were first set in the wax model, forms an anchor for those teeth, holding them in proper position with relation to each other during the time the porcelain is being placed in the mold and until the porcelain is fused.

The furnace is heated until the porcelain fuses and thereafter the mold members may be forced together to give the porcelain the exact shape of the mold.

I claim as my invention:

1. An investment gredient which expands and alumina whic contracts at high temperature, said ingredients being mixed in such proportions that material havlng an in the expansion of the one compensates for 4 the contraction of noappreciable change in the volume of the mass.

2. An investment material consisting of silica and alumina particles in such proporthe other so that there is amaool I I a such proportions that the alumina shall act sistance, and great mechanical strength, and as a bonding material and the expansion of enabling a mould formed out of the investthe silica upon the application of intense ment material to be readily removed after 15 heat to the mass shall oflset the contraction fusion of the article moulded.

5 of the alumina, the whole retaining its Des Moines, Iowa, June 16, 1922.

original volume without appreciable change,

having unusual porosity, high thermal re- ARTHUR ARSHALL oINTOS H. 

